1. Field of the Invention
The present invention relates to an optical system for a projector using a digital mirror device, a projection method using the same and, more particularly, to an optical system using a modified light integrator capable of correcting the keystone phenomenon on light projected onto a digital mirror device panel, and a projection method using the same, wherein the keystone phenomenon refers to a phenomenon transforming an original shape on a projection surface due to the magnitude of an incident angle.
2. Description of the Related Art
A digital light processing (“DLP”) projector, using a digital mirror device, generally eliminates the pixel mosaic problem of a liquid crystal display (“LCD”)
projector and delivers a higher contrast ratio so as to enhance original color reproducibility, thereby enabling highly bright, clear, and large color images to be obtained in, for example, presentations for use in businesses, schools, and advertisements, or in entertainment fields such as movies.
FIG. 1 is a schematic view showing a conventional optical system for a digital mirror device projector.
As shown in FIG. 1, a conventional digital mirror device projector has a light source 10; an ellipsoidal reflector 11 for reflecting and collecting beams emitted from the light source 10; a color filter wheel 12 for separating a white light collected from the ellipsoidal reflector 11 into red (“R”), green (“G”), and blue (“B”) colors, and for illuminating the R, G, or B color, respectively, by one-third of the light per frame; a light integrator 13 for receiving light radiated, by color, from the color filter wheel 12, transforming the cross-sectional face of the output light into a predefined desired shape, and making the amount of light uniform; a lens group 14 for magnifying and radiating the light emitted from the light integrator 13; a reflection prism 15 for reflecting and radiating the light, by color, emitted from the lens group 14 to a digital mirror device panel 16 at a predetermined incidence angle (about 24 degrees), wherein the digital mirror device panel 16 is for adjusting a reflection angle, by pixel, and modulating an image formed by the light radiated from the reflection prism 15; and a projection lens 17 for projecting onto a screen 18 the image modulated by the digital mirror device panel 16.
The digital mirror device panel 16 is a combination of devices known as Micro Electro Mechanical (“MEM”) systems, and is formed with pressure sensors, accelerometers, and micro actuators.
FIG. 2 is a perspective view showing a general structure of a reflector for a digital mirror device panel 16.
The digital mirror device panel 16 consists of a combination of Complementary Metal Oxide Semiconductor (“CMOS”) cells of single crystal on a CMOS. Such a CMOS cell has an aluminum mirror 21 of about 16 μm2 in area over it. Further, the aluminum mirror 21 can rotate about a rotation axis, depending upon the state of a basic memory cell, and can reflect light in one or two directions. Such rotations of the aluminum mirror 21 are made due to electrostatic attractions caused by voltage differences formed between the aluminum mirror 21 and the basic memory cell. When the memory cell is turned on, the aluminum mirror 21 rotates +12 degrees to reflect incident light inside the projection lens 17 and, when turned off, the aluminum mirror 21 rotates −12 degrees to reflect the incident light outside the projection lens 17.
In the conventional optical system described above, when output light formed from the light integrator 13 is projected on the digital mirror device panel 16, light incident from the reflection prism 15 is modulated and reflected to the projection lens 17 by the combination of respective aluminum mirrors 21 of the digital mirror device panel 16.
However, in the conventional optical system described above, if the light emitted from the reflection prism 15 becomes incident at, for example, 24° (that is twice the rotation angle of the aluminum mirror 21), when incident on the digital mirror device panel 16, the keystone phenomenon occurs in a direction vertical to the rotation axis of the aluminum mirror 21, causing the problem that the original shape of the cross-sectional face of the output light from the light integrator 13 is transformed.
FIG. 3A is a cross-sectional view of a conventional light integrator 13, and FIG. 3B is a view showing the shape of the light emitted from the light integrator 13 of FIG. 3A and projected onto the digital mirror device panel 16.
As shown in FIG. 3A and FIG. 3B, such transformation results in an insufficiency in the amount of light at corner portions of the digital mirror device panel 16, and causes the problem of lowering the radiation efficiency of the light emitted from the light source 10.